This proposal represents a new research direction on HCMV entry glycoproteins for the Jardetzky Laboratory, which has previously had extensive prior effort focusing on understanding Epstein-Barr virus (EBV) entry into target cells and on developing novel approaches to therapeutic intervention. The entry of HCMV into epithelial and endothelial cells requires the formation of a pentameric viral glycoprotein complex comprised of the gH, gL, UL128, UL130, and UL131 proteins (gHgL/UL128-131). This pentameric complex is a functional analog of the EBV gHgL/gp42 complex, which targets EBV to infect B cells. HCMV gHgL also assembles into a trimeric complex with the gO protein, which has a broader functional role, affecting virus entry into fibroblasts, epithelial cells and endothelial cells. Th Jardetzky Laboratory has conducted extensive crystallographic and functional studies of the EBV gHgL and gp42 complexes and demonstrated that EBV infection can be blocked with a gp42-derived high affinity peptide inhibitor. We now propose to conduct similar studies of the HCMV gHgL, gHgL/gO and gHgL/UL128-131 complexes, as well as examine the interaction of HCMV gHgL complexes with neutralizing antibodies. These studies will further our understanding of herpesvirus entry mechanisms and may lead to new routes to developing HCMV entry inhibitors or gHgL subunit vaccines.